But for instance, the below gives you shadows and radiused corners. I just copied from the CSS on @Piranha1605 Black Boxes example and dropped it in my custom.css file.
Just delete modules you don’t have, add ones you do have.
For me that meant deleting newsfeed, compliments and both the weatherforecast and currentweather since the weather module takes place of current and forecast.

/**

• module.color_border_shadow
  */
  .module.clock,
  .module.calendar,
  .module.newsfeed,
  .module.weatherforecast,
  .module.currentweather,
  .module.compliments {
  padding:8px;
  border-radius: 10px;
  box-shadow: 0 2em 6em #000;
  background: transparent;
  }

So mine is:
module.clock
module.calendar
module.weather
module.MMM-SmartWebDisplay {
padding:8px;
border-radius: 15px;
box-shadow: 0 2em 6em #000;
background: transparent;
}

The iFrame was a roll of dice on my part but it worked with no problems

I increased border-radius: to 15px (I think) but may be 12px and got more of a radius than in the original example.

I copy/pasted his header from the #3 example neomorphism to get the headers on the weather and calendar to get shadowed look. Clock has no header so no effect.